1. Field of the Invention
The present invention relates to a thin film transistor and a display device which operates using the thin film transistor.
2. Description of the Related Art
As one type of field-effect transistor, a thin film transistor whose channel region is formed using a semiconductor layer that is formed over a substrate having an insulating surface is known. Techniques for using amorphous silicon, microcrystalline silicon, and polycrystalline silicon for semiconductor layers in thin film transistors have been disclosed (see References 1 to 5). A typical application of thin film transistors is a liquid crystal display television device, in which thin film transistors have been put to practical use as a switching transistor for each pixel that constitutes a display screen.    [Reference 1] Japanese Published Patent Application No. 2001-053283    [Reference 2] Japanese Published Patent Application No. H5-129608    [Reference 3] Japanese Published Patent Application No. 2005-049832    [Reference 4] Japanese Published Patent Application No. H7-131030    [Reference 5] Japanese Published Patent Application No. 2005-191546